This invention relates to a method of chlorinating the side chains of toluene, xylenes, or mesitylenes. In particular, it relates to a method in which a portion of the aromatic compound is incompletely side chain chlorinated, the unreacted aromatic compound is separated from the incompletely side chain chlorinated aromatic compound, and the incompletely side chain chlorinated aromatic compound is further side chain chlorinated.
.alpha.,.alpha.,.alpha.,.alpha.',.alpha.',.alpha.'-hexachloro-m-xylene (HCMX) is used to make fluorinated solvents and other chemicals. It is made by chlorinating m-xylene. (See, for example, U.S. Pat. No. 4,029,560.) While chlorinating m-xylene is effective in making HCMX, it can result in 40 to 50% of the product being ring chlorinated when run as a continuous process; the ring chlorinated material is disposed of as waste.